Kidney stones usually form when crystalline minerals – normally flushed away in the urine – stick together to form clumps, ranging in size from a grain of sand to coarse gravel. The cause may be gout or another metabolic problem, or it may be a structural or metabolic abnormality within the kidney. When kidney stones block any part of the urinary system, especially the ureters or bladder, they cause intense pain. Stones may pass through the system; others must be removed surgically or by sound-wave treatment (lithotripsy).
In order to prevent recurrences, it is important to determine the cause of the kidney stones. Most are formed of calcium oxalate or calcium phosphate. Less commonly, stones may form from uric acid crystals, especially in those people who suffer from gout. A fourth type, cystine stones, occurs in fairly rare metabolic diseases.
Fluids, fluids and more fluids. Regardless of the type of stone, it’s essential to drink enough liquids to maintain fluid balance and flush away the minerals that accumulate to form stones. Most people with stones could reduce the risk of recurrence by increasing their water intake so that they excrete about 2 litres of urine a day.
Although most stones contain calcium, it’s not a good idea to cut down on dietary calcium unless your doctor specifically orders it. Restricting calcium in the diet may actually increase the incidence of stones in some people, whereas a high-calcium diet has been shown to reduce it. Make sure you get a good intake of calcium from your food. If the body fails to get enough calcium, it will rob the bones in order to get the mineral, thus increasing the danger of osteoporosis.
Phosphorus-rich foods contribute to the formation of calcium phosphate stones. Phosphorus is found in high quality protein. The balance of phosphorus and calcium in the diet is very delicate, however, and restricting the intake of one may interfere with the other. Take advice from a doctor or dietitian when changing your intake of either essential mineral in order to maintain balanced nutrition.
Finding a Balance
Foods high in oxalate. Oxalate-rich foods include rhubarb, nuts, beetroot, tofu, chocolate, tea, berries, red currants, tangerines, wheatbran and wheatgerm, most of the dark green leafy vegetables, sweet potatoes, baked beans, lentils and beer. Many people believe that these foods must be avoided, but this is unnecessary and eliminating all these foods would deplete the diet of essential vitamins and minerals. A doctor or dietitian will provide a list of foods that can be eaten in moderation with little risk of causing a recurrence. People with gout should keep to a low-fat diet to reduce the risk of uric acid stones.
Kidney stones are rare in strict vegetarians. While the connection between stones and protein is not fully understood, it is known that protein increases the acidity of urine, which probably plays a role. Many people could reduce the risk of recurrence of stones by cutting their daily protein intake to between 0.8 and 1.0g per kilogram of body weight. It’s easier to reduce protein intake if you cut down on animal products. Eating a variety of foods such as rice and beans can supply the essential amino acids.